PDFPatcher/App/Model/PdfModelHelper.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Text;
using iTextSharp.text.pdf;

namespace PDFPatcher.Model
{
	static class PdfModelHelper
	{
		internal static T Locate<T>(this PdfDictionary source, params object[] path) where T : PdfObject {
			PdfObject s = source;
			if (s == null) {
				return null;
			}
			PdfName n;
			foreach (var item in path) {
				n = item as PdfName;
				if (s == null) {
					return null;
				}
				if (n != null) {
					if (s.Type != PdfObject.DICTIONARY && s.Type != PdfObject.STREAM) {
						return null;
					}
					s = (s as PdfDictionary).GetDirectObject(n);
					continue;
				}
				if (item is not int) {
					throw new ArgumentException("参数类型必须为 Int32 或 PdfName");
				}
				int i = (int)item;
				if (s.Type != PdfObject.ARRAY) {
					return null;
				}
				s = (s as PdfArray).GetDirectObject(i);
			}
			return s as T;
		}
		internal static T Locate<T>(this PdfDictionary source, params PdfName[] path) where T : PdfObject {
			return source.Locate<T>(true, path);
		}
		internal static T Locate<T>(this PdfDictionary source, bool resolveRef, params PdfName[] path) where T : PdfObject {
			PdfObject o = null;
			foreach (var item in path) {
				if (source == null) {
					return null;
				}
				o = resolveRef ? source.GetDirectObject(item) : source.Get(item);
				source = o as PdfDictionary;
			}
			return o as T;
		}
		internal static T Locate<T>(this PdfArray source, int index) where T : PdfObject {
			return source.Locate<T>(true, index);
		}
		internal static T Locate<T>(this PdfArray source, bool resolveRef, int index) where T : PdfObject {
			if (source == null) {
				return null;
			}
			return (resolveRef ? source.GetDirectObject(index) : source[index]) as T;
		}
		internal static T CastAs<T>(this PdfIndirectReference pdfRef) where T : PdfObject {
			return PdfReader.GetPdfObject(pdfRef) as T;
		}
		internal static float ValueAsFloat(this PdfObject obj) {
			return obj is PdfNumber n
				? n.FloatValue
				: 0;
		}
		internal static float ValueAsInt(this PdfObject obj) {
			return obj is PdfNumber n
				? n.IntValue
				: 0;
		}

		internal static bool ValueIs(this PdfNumber obj, double value) {
			return obj != null && obj.DoubleValue == value;
		}
		internal static bool ValueIs(this PdfBoolean obj, bool value) {
			return obj != null && obj.BooleanValue == value;
		}
		internal static bool ValueIs(this PdfObject obj, PdfName value) {
			return value.Equals(obj);
		}

		internal static int TryGetInt32(this PdfDictionary source, PdfName key, int defaultValue) {
			var w = source.GetAsNumber(key);
			return w?.IntValue ?? defaultValue;
		}
		internal static bool TryGetBoolean(this PdfDictionary source, PdfName key, bool defaultValue) {
			var b = source.GetAsBoolean(key);
			return b?.BooleanValue ?? defaultValue;
		}

		internal static string Decode(this PdfString text, Encoding encoding) {
			if (text == null) {
				return String.Empty;
			}
			var bytes = text.GetBytes();
			using (MemoryStream ms = new MemoryStream(bytes)) {
				if (encoding == null) {
					if (bytes.Length >= 2 && (bytes[0] == 0xFF && bytes[1] == 0xFE || bytes[0] == 0xFE && bytes[1] == 0xFF)) {
						using (TextReader r = new StreamReader(ms, true)) {
							return r.ReadToEnd();
						}
					}
					else {
						return PdfEncodings.ConvertToString(bytes, PdfObject.TEXT_PDFDOCENCODING);
					}
				}
				else {
					// 忽略字节顺序标记
					if (bytes.Length >= 2 && (bytes[0] == 0xFF && bytes[1] == 0xFE || bytes[0] == 0xFE && bytes[1] == 0xFF)) {
						ms.Position += 2;
					}
					else if (bytes.Length >= 3 && bytes[0] == 0xef && bytes[1] == 0xbb && bytes[2] == 0xbf) {
						ms.Position += 3;
					}
					else if (bytes.Length >= 4 && bytes[0] == 0 && bytes[1] == 0 && bytes[2] == 0xfe && bytes[3] == 0xff) {
						ms.Position += 4;
					}
					using (TextReader r = new StreamReader(ms, encoding)) {
						return r.ReadToEnd();
					}
				}
			}
		}

		internal static PdfString ToPdfString(this string text) {
			if (String.IsNullOrEmpty(text)) {
				return new PdfString();
			}
			bool u = false;
			foreach (var c in text) {
				if (c > 127) {
					u = true;
					break;
				}
			}
			return u ? new PdfString(text, PdfObject.TEXT_UNICODE) : new PdfString(text);
		}

		internal static IEnumerable<ResourceReference> GetReferencedResources(PdfDictionary source, Predicate<PdfDictionary> predicate, HashSet<PdfIndirectReference> refDedup) {
			foreach (var item in source) {
				if (item.Value is PdfIndirectReference r
					&& refDedup.Add(r)
					&& PdfReader.GetPdfObjectRelease(r) is PdfDictionary o) {
					if (predicate(o)) {
						yield return new ResourceReference(r, item.Key, o);
					}
					foreach (var f in GetReferencedResources(o, predicate, refDedup)) {
						yield return f;
					}
				}
				else if (item.Value is PdfDictionary d) {
					foreach (var f in GetReferencedResources(d, predicate, refDedup)) {
						yield return f;
					}
				}
			}
		}
	}
}